We will use an extracorporeal silicone membrane lung for prolonged partial veno-venous and veno-arterial respiratory blood gas exchange of potentially salvageable patients dying of acute respiratory failure. Perfusion can rapidly correct hypoxia and hypercapnea, eliminate the need for dangerously high inspired oxygen concentrations and inflation pressures, and allow pulmonary repair without additional physiologic insult. We hope to identify types of acute pulmonary failure responsive to extracorporeal perfusion and to determine criteria for the optimum time to initiate extracorporeal support. Perfusion will be carried out in a fully equippped and staffed unit specializing in the therapy of acute respiratory failure. The disposable fixed priming volume, spiral coil silicone membrane lung will be used. This membrane lung has been uniquely benign and reliable when used for animal and clinical perfusions lasting more than one week. Prior to clinical use, new models of the spiral coil membrane lung will be tested in sheep. However, both heparin bonding to silicone rubber and minimal systemic doses of heparin are potentially valuable techniques that need to be tested in an animal whose coagulation system more closely resembles man than that of sheep. We will therefore use a primate model for our basic investigations of the natural history of pulmonary recovery through veno-venous and veno-arterial perfusions. These proposed studies should allow a more rational and safer choice of perfusion techniques that may save patients with acute respiratory failure.